U.S. patent number 4,620,553 [Application Number 06/733,857] was granted by the patent office on 1986-11-04 for tobacco smoke filters.
This patent grant is currently assigned to Imperial Group Public Limited Company. Invention is credited to Christopher R. Bale, Beresford R. Gill.
United States Patent |
4,620,553 |
Bale , et al. |
November 4, 1986 |
Tobacco smoke filters
Abstract
A filter for a smoking article employing a resilient valve
assembly in the path of the smoke. The valve assembly being movable
in a first position in which the flow ventilating air is permitted
and a second position in which the flow of air is prevented. The
valve assembly being resiliently biased towards the first position
and being displaceable towards the second position when a
particular pressure differential is exceeded.
Inventors: |
Bale; Christopher R. (Keynsham,
GB2), Gill; Beresford R. (Paulton, Nr. Bristol,
GB2) |
Assignee: |
Imperial Group Public Limited
Company (London, GB2)
|
Family
ID: |
26287770 |
Appl.
No.: |
06/733,857 |
Filed: |
May 14, 1985 |
Foreign Application Priority Data
|
|
|
|
|
May 22, 1984 [GB] |
|
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8413017 |
May 22, 1984 [GB] |
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8413018 |
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Current U.S.
Class: |
131/198.1;
131/215.1; 131/215.2; 131/215.3; 131/336 |
Current CPC
Class: |
A24D
3/041 (20130101) |
Current International
Class: |
A24D
3/00 (20060101); A24D 3/04 (20060101); A24D
003/04 () |
Field of
Search: |
;131/336,215.1,215.2,215.3,198.1,198.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Millin; V.
Attorney, Agent or Firm: Larson and Taylor
Claims
We claim:
1. For attachment to a rod of smokable material, an improved filter
assembly of the type, wherein ventilation is provided for a cavity
associated with the rod so that combustion products from said rod
are intermingled with ventilation air in said cavity before
proceeding to a user, the improvement comprising,
(a) first and second axially spaced cylindrical filter plug
elements,
(b) a cylindrical tube of air-impervious material open at both ends
connecting said filter elements and in axial alignment with said
filter elements, the tube including at least one ventilating
aperture therein,
(c) a tipping wrapper encasing the cylindrical surfaces of the
filter elements and the tube, and including ventilation means
overlying said at least one ventilating aperture, and,
(d) resilient valve means for preventing the passage of ventilating
air through said at least one ventilating aperture when a
predetermined pressure differential between the ventilating air
flow through said at least one ventilating aperture and the flow of
combustion products through the tube is exceeded, and for
permitting the passage of ventilating air through said at least one
ventilating aperture when said pressure differential is not
exceeded, said resilient valve means being movable between a first
position in which the flow of ventilating air through said
ventilation aperture is permitted and a second position in which
the flow of air through said ventilation aperture is prevented,
said valve means being resiliently biased towards said first
position and being displaceable towards said second position when
said pressure differential is exceeded.
2. A filter assembly as claimed in claim 1 wherein the resilient
valve means comprises a resiliently mounted piston axially slidable
within the tube so as to be resiliently urged from a said second
position towards a said first position in the tube, the piston
having a crown provided with an aperture therein to permit the
passage of combustion products therethrough, the piston, in said
second position thereof, acting to seal off said at least one
ventilating aperture and in said first position thereof, acting to
uncover said at least one ventilating aperture uncovered by the
piston, the resilient mounting of the piston being such as to urge
the piston from the first region towards the second region and the
resilience of the mounting being such that a predetermined flow of
combustion products through the assembly will overcome the
resilience so as to re-position the piston in the first region.
3. A filter assembly as claimed in claim 2 wherein the resilient
mounting of the piston is provided by a compression spring
effecting a connection between the base of the piston and a face of
the second filter element.
4. A filter assembly as claimed in claim 3 wherein the compression
spring comprises a filament spring.
5. A filter assembly as claimed in claim 2 wherein the piston and
the resilient mounting therefor are a one-piece moulding of plastic
material.
6. A filter assembly as claimed in claim 2 wherein the resilient
valve means comprises a flap valve means associated with said at
least one ventilating aperture.
7. A filter assembly as claimed in claim 6 wherein the flap valve
means comprises by a pair of overlapping members, one of which is
flexible, each member being provided by an end portion of a
respective one of a pair of opposed hollow cylinders of a synthetic
resin located within and coaxial with the tube.
8. A filter assembly as claimed in claim 7 wherein each overlapping
member tapers towards its free end.
9. A filter assembly as claimed in claim 1 wherein the tube is
provided with a circumferential channel in its outer surface, such
that said at least one ventilating aperture lies in the base of the
channel and provides communication between the channel and the
interior of the tube, and the ventilation means of the tipping
wrapper overlies the channel.
10. A filter assembly as claimed in claim 1 wherein the ventilation
means in the tipping wrapper comprises a circumferential series of
ventilation holes.
11. A filter assembly as claimed in claim 1 wherein a series of
said at least one ventilating apertures are spaced
circumferentially round the tube.
12. A cigarette comprising the combination of a wrapped rod of
smokable material with a filter assembly as claimed in claim 1.
13. A filter assembly as claimed in claim 1 wherein the ventilation
means in the tipping wrapper comprises a circumferential region of
high porosity paper.
Description
This invention concerns improvements in or relating to a filter
assembly for an elongate smoking article, in particular to an
improved ventilated filter assembly for a cigarette.
It is known to provide ventilation into a cavity in a cigarette
filter so that smoke passing into the filter from burning tobacco
will intermingle with ventilating air in the cavity before
proceeding to the smoker's mouth. Such a filter will be referred to
as "of the type described".
A disadvantage of ventilated filters is that the smoker is unable
to control the degree of ventilation and hence the ratio of smoke
to ventilating air entering the smoker's mouth.
The present invention enables the smoker to exert a measure of
control over the ratio of smoke to ventilating air in the cavity of
a filter of the type described.
According to a first aspect of the present invention there is
provided, for attachment to a rod of smokable material, a filter
assembly of the type described, comprising,
(a) first and second axially spaced cylindrical filter plug
elements so arranged that when the assembly is attached to the rod
of smokable material the first element is adjacent the rod,
(b) a tube of air-impervious material open at both ends separating
and in axial alignment with said filter elements, the tube being
provided in its cylindrical wall with at least one ventilating
aperture,
(c) a tipping wrapper encasing the cylindrical surfaces of the
filter elements and the tube, the tipping wrapper being provided
with ventilation means overlying said at least one ventilating
aperture, and
(d) resilient valve means adapted to prevent the passage of
ventilating air through said at least one ventilating aperture when
a predetermined pressure differential between the ventilating air
flow through said at least one ventilating aperture and the flow of
combustion products through the tube is exceeded, and to permit the
passage of ventilating air through said at least one ventilating
aperture when said pressure differential is not exceeded.
In a first embodiment of the invention the resilient valve means
may be provided by a resiliently mounted piston axially slidable
within the tube, the piston being provided with an aperture in its
crown to permit the passage of combustion products therethrough,
the arrangement being such that when the piston is located in a
first region of the tube the piston will seal off said at least one
ventilating aperture and when the piston is located in a second
region of the tube between the first region and the first filter
element said at least one ventilating aperture will be uncovered by
the piston, the resilient mounting of the piston being such as to
urge the piston from the first region towards the second region and
the resilience of the mounting being such that a predetermined flow
of combustion products through the assembly will overcome the
resilience so as to re-position the piston in the first region.
The resilient mounting of the piston is preferably provided by a
compression spring effecting a connection between the base of the
piston and a face of the second filter element.
The compression spring may be a filament spring.
The piston and the resilient mounting are preferably a one-piece
moulding of plastics material.
In a second embodiment of the invention the resilient valve means
may be a flap valve means associated with said at least one
ventilating aperture.
The flap valve means is preferably provided by a pair of
overlapping members, one of which is flexible, each member being
provided by an end portion of a respective one of a pair of opposed
hollow cylinders of synthetic resin located within and coaxial with
the tube.
Each overlapping number preferably tapers towards its free end.
The tube is preferably provided with a circumferential channel in
its outer surface, such that said at least one ventilating aperture
lies in the base of the channel and provides communication between
the channel and the interior of the tube, and the ventilation means
of the tipping wrapper overlies the channel.
The ventilation means in the tipping wrapper is peferably provided
by a circumferential series of ventilation holes or by a
circumferential region of high porosity paper.
Preferably there is provided a series of said at least one
ventilating apertures spaced circumferentially round the tube.
According to a second aspect of the present invention there is
provided a cigarette comprising the combination of a wrapped rod of
smokable material with a filter assembly according to the first
aspect of the invention.
The invention will now be described by way of example only with
reference to the accompanying diagrammatic drawings in which,
FIG. 1 is a perspective view of a cigarette including a wrapped
tobacco rod and a partially unwrapped filter assembly according to
the invention;
FIG. 2 is a longitudinal cross-section through a first embodiment
of an assembled cigarette according to FIG. 1;
FIG. 3 is a longitudinal cross-section through a second embodiment
of an assembled cigarette according to FIG. 1;
FIG. 4 is a detail view of a portion of the filter assembly shown
in FIG. 3; and,
FIG. 5 is an exploded perspective view of two hollow cylindrical
components of the filter assembly of FIG. 3.
Referring to FIG. 1 of the drawings there is shown a cigarette 10
comprising a cylindrical tobacco rod 12 wrapped in cigarette paper
14, and a filter assembly 20 attached to the tobacco rod.
The filter assembly 20 comprises two spaced coaxial cylindrical
filter elements 22, 24 of cellulose acetate fibre wrapped in
plugwrap 26, and, separating the filter elements, an impervious
synthetic resin tube 28, open at both ends, coaxial with, and of
the same diameter as, the filter elements. The tube 28 thus
provides a chamber 30 (not visible in FIG. 1) between facing ends
of the filter elements 22, 24.
The tube 28 and the filter elements 22, 24 are wrapped in tipping
paper 16 which is used to attach the filter assembly to the tobacco
rod in a manner common in the art so that filter element 22 abuts
the tobacco rod 12.
The tube 28 is provided about half-way along its length with a
circumferential channel 32 in its outer surface. The floor of the
channel 32 is provided with a number of apertures 34 spaced evenly
round the circumference of the tube and communicating with the
chamber 30. The tipping paper 16 is provided with a circumferential
series of vents 36 which overlie the channel 32. Clearly, in the
absence of obstructions, ventilating air is able to pass through
the tipping paper and through the base of the channel 32 into the
chamber 30 when the smoker draws on the cigarette.
Referring now to a first embodiment of the invention which is
described with reference to FIGS. 1 and 2, there is shown, slidably
mounted within the tube 28, a piston 40 made of synthetic resin.
The piston 40 has a crown 42, and a skirt 44 extending towards
filter element 24 (i.e. the filter element at the mouth end of the
assembly). The crown 42 is provided with at least a pair of
apertures 45, providing means for tobacco combustion products to
flow through the piston from the upstream (i.e. the tobacco end) of
the chamber 30 to the downstream end (i.e. mouth end) of the
chamber 30.
Unrestricted, the piston 40 would naturally slide the length of the
chamber 30 when a smoker draws on the cigarette, and the depth of
the skirt 44 is designed so that when the crown of the piston has
travelled about one quarter of the length of the chamber 30 from
filter element 22 the apertures 34 in the base of the channel 32
become occluded by the skirt 44 and remain in that condition until
and while the piston skirt contacts the inner face of filter
element 24.
However, there is provided, moulded to the underside of the piston
crown 42, a resilient filament spring 46 which extends along the
axis of the chamber 30 to abut the inner face of filter element 24.
Movement of the piston 40 towards the mouth end of the filter
assembly is therefore resisted by the resilience of the spring
46.
The effect of the above arrangement is that, when a smoker draws on
a lighted cigarette incorporating the filter assembly of the
invention, combustion products are drawn through filter element 22
into the chamber 30 and ventilating air is simultaneously drawn
through the vents 36 into the chamber. However, the flow of
combustion products into the chamber 30 will tend to move the
piston towards the mouth end of the chamber. At low levels of draw
this movement is prevented by the spring 46 and so both combustion
products and ventilating air will enter the chamber 30. At high
levels of draw the flow of combustion products will overcome the
resistance offered by the resilience of the spring 46 and will move
the piston mouthwards to a position where the piston skirt 44 will
occlude or otherwise shut off the ventilating apertures 34 and
prevent ventilating air from entering the chamber.
It is convenient to ensure adequate abutment of the spring 46
against the inner face of filter element 24 by fixing the free end
of the spring to the filter element by a small amount of adhesive
48. The spring 46 may alternatively be of a shape other than
filamentary, e.g. a coil spring.
Referring now to a second embodiment of the invention which is
described with reference to FIGS. 1 and 3 to 5 of the drawings,
there is shown, located within the tube 28, and abutting its inside
surface and coaxial therewith, two hollow cylinders 50, 52 made of
a synthetic plastics material such as polypropylene. An end of one
cylinder 50 abuts the inner face of filter element 24, and likewise
an end of the other cylinder 52 abuts the inner face of filter
element 22. The other ends 54, 56 of the cylinders 50, 52 are
respectively located in the vicinity of the apertures 34 in the
tube 28. Each of these ends 54, 56 is cut into a circumferential
series of longitudinal flaps 60, 62 by a series of slots 64, 66
parallel to the axis of each cylinder 50, 52 respectively and
extending longitudinally along the cylinders from the ends 54, 56
respectively, as shown in FIG. 5. The thickness of each flap 60, 62
tapers from the full wall thickness of its respective cylinder
longitudinally towards its respective end 54, 56.
The lengths of the cylinders 50, 52 are such that the flaps 60, 62
overlap each other immediately over the apertures 34 in the tube
28. Further, the flaps are shaped so that when they overlap there
will normally be a space 68 (FIG. 4) between their adjacent
surfaces. Accordingly, ventilating air will be able to follow the
path into the chamber 30 indicated by arrows 9 in FIG. 4.
The flexibility of the flaps 60, 62 is such that if the flow of the
tobacco combustion products in the chamber 30 results in a pressure
differential in the chamber greater by a predetermined amount than
that exerted by the incoming ventilating air on flap 60 then the
pressure within the chamber 30 will close flap 60 against flap 62,
thereby occluding or shutting off aperture 34, and thus prevent
ventilating air from entering the chamber.
The resilience of the flaps 60, 62 is such that when the pressure
in the chamber 30 is reduced then the flaps 60, 62 part and permit
ventilating air to re-enter the chamber through the aperture 34.
Flaps 60, 62 thus act as flap valves.
The effect of the arrangement of the second embodiment described
above is that when a smoker draws on a lighted cigarette
incorporating the filter assembly of the invention combustion
products are drawn through filter element 22 into the chamber 30
and ventilating air is simultaneously drawn through the vents 36
into the chamber where it mixes with the combustion products. The
mixture then passes through filter element 24 into the smoker's
mouth. At low levels of draw there is no restriction on the ingress
of ventilating air through the flap valves 60, 62. At high levels
of draw, however, the flow of combustion products in the chamber 30
increases the pressure against flaps 60 and causes them to close on
flaps 62 and thus prevent further ventilating air from entering the
filter.
Alternative forms of the second embodiment may provide alternative
designs of flap means controlled by the pressure in the chamber 30,
for governing the amount of ventilating air delivered to the filter
assembly.
It is part of the practice of smoking a cigarette that a smoker
will tend to take a relatively heavy draw on the cigarette at the
commencement of a smoke so that substantial quantities of
ventilating air are drawn in through the cigarette paper 14
downstream of the burning tip, thus ensuring a cool organoleptic
effect. As the unsmoked length of tobacco diminishes, a
correspondingly smaller amount of ventilating air gets through the
cigarette paper 14 and the smoker naturally tends to take lighter
draws on the cigarette.
If these phenomena are considered in the light of the present
invention it will be appreciated that at the commencement of a
smoke, when the smoker takes a heavy draw on the cigarette, the
pressure differential inside the filter assembly will cut off the
air ventilation system of the filter itself, either, as in the
first embodiment, by causing the piston skirt 44 to occlude the
apertures 34, or, as in the second embodiment, by causing flaps 60
to close on flaps 62, and the smoker will experience only the air
entering the cigarette through the cigarette paper.
However, at a later stage in the smoking of the cigarette, when
relatively little ventilating air is being drawn in through the
cigarette paper, and the smoker is taking light draws on the
cigarette, the reduced pressure in the filter assembly will now
permit extra ventilating air to enter through the side apertures of
the filter, either, as in the first embodiment, because the
resilience of the filament spring 46 moves the piston away from its
occluding relationship with the apertures 34, or, as in the second
embodiment, because the reduced pressure permits the flaps 60, 62
to part. The smoker is thus enabled to get more ventilating air
than he would otherwise have expected and therefore continues to
experience a cool organoleptic effect.
In some applications of the invention is will be convenient to
dispense with the circumferential channel 32, so that the vents 36
in the tipping paper 16 deliver ventilating air directly to the
apertures 34.
The synthetic resins or plastics materials used in the filter
assembly of the present invention will be synthetic polymers chosen
for their thermal and chemical stability under smoking conditions,
and for their physiological inertness. Typical resins or plastics
materials contemplated in the invention are olefinic polymers, such
as polypropylene.
* * * * *